MEMS mirror element

Abstract

To provide an MEMS mirror element with which it is possible to increase the amplitude of a mirror without taking measures to lower a frequency when oscillating the mirror, reduce the size of the mirror, and increase the size of the MEMS mirror element due to the increased size of actuators.SOLUTION: The MEMS mirror element is characterized by comprising: a movable mirror unit 10 including a mirror unit 11 and a pair of torsion bars 12 for supporting the mirror unit 11 swingably around a rotation axis S, one end of which is connected to the mirror unit 11, and which extends along the rotation axis S; a pair of connection units 41 to which the respective other ends of the pair of torsion bars 12 are connected; a first actuator 20 connected to the pair of connection units 41 and located in the periphery of the movable mirror unit 10; and a second actuator 30 connected to the pair of connection units 41 and located in the periphery of the movable mirror unit 10 and the first actuator 20.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a MEMS mirror element.

Background Art

[0002] As a device using semiconductor manufacturing technology, MEMS (Micro Electro Mechanical Systems) is known. Patent Document 1 discloses a MEMS optical deflector in which a rigidity-changing piezoelectric element is arranged at a location where stress concentrates in order to improve the durability of a torsion bar connected to a mirror portion. Patent Document 2 discloses a MEMS device provided with a desiccant that absorbs moisture that has passed through a passivation film in order to suppress deterioration of a piezoelectric film layer due to moisture that has passed through the passivation film. Patent Document 3 discloses a MEMS optical scanner that enables setting or adjusting the deflection angle of a mirror by adjusting an AC voltage value or the like in order to drive the mirror at a large deflection angle. Patent Document 4 discloses a MEMS device provided with a gap having a width that allows air to move, together with a gap required for a movable part to move, near a location where the movable range of the movable part is large in order to suppress noise. Patent Document 5 discloses a MEMS mirror device in which a first beam that connects an inner movable member and a frame body is arranged on the back surface of a reflective mirror member for miniaturization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] A MEMS mirror element is used, for example, in a laser scanning system to scan laser light that is spot-irradiated from a laser light source. In order to scan the laser light over a wider range, it is required to increase the amplitude when swinging the mirror provided in the MEMS mirror element. However, in a conventional MEMS mirror element, one actuator is provided for one mirror. For this reason, in order to increase the amplitude of the mirror, there are problems that require measures such as lowering the frequency when swinging the mirror, miniaturizing the mirror, and increasing the size of the MEMS mirror element as the actuator is enlarged.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a MEMS mirror element capable of increasing the amplitude of a mirror without taking measures such as lowering the frequency when swinging the mirror, miniaturizing the mirror, and increasing the size of the MEMS mirror element as the actuator is enlarged.

Means for Solving the Problems

[0006] <1>A MEMS mirror element according to Embodiment 1 of the present invention includes a mirror portion, a pair of torsion bars that rotatably support the mirror portion around a rotation axis, one end of which is connected to the mirror portion and extends along the rotation axis, a movable mirror portion including the torsion bars, a pair of connection portions to which the other ends of the pair of torsion bars are connected, a first actuator connected to the pair of connection portions and disposed around the movable mirror portion, and a second actuator connected to the pair of connection portions and disposed around the movable mirror portion and the first actuator.

[0007] According to the invention related to aspect 1, it includes a first actuator disposed around the movable mirror part, and a second actuator disposed around the movable mirror part and the first actuator. That is, the MEMS mirror element includes two actuators for one movable mirror part. Thereby, for example, compared with the case where the MEMS mirror element includes one actuator for one movable mirror part, the force for swinging the mirror part can be increased. Therefore, for example, the speed when the mirror part swings can be increased. Accordingly, without taking measures such as reducing the frequency when swinging the mirror part, miniaturizing the mirror part, or increasing the size of the MEMS mirror element as the size of the actuator increases, the amplitude of the mirror part can be increased.

[0008] <2>The MEMS mirror element according to aspect 2 of the present invention is the MEMS mirror element according to aspect 1, wherein the first actuator includes semi-circular parts provided in a pair on one side and the other side in a direction perpendicular to the rotation axis, and both ends of each of the pair of semi-circular parts in the direction along the rotation axis are connected to each of the pair of connection parts, and the inner contour parts of each of the pair of semi-circular parts are along the outer contour of the mirror part.

[0009] According to the invention related to aspect 2, the first actuator includes semi-circular parts provided in a pair on one side and the other side in a direction perpendicular to the rotation axis. Both ends of each of the pair of semi-circular parts in the direction along the rotation axis are connected to each of the pair of connection parts. Thereby, each of the semi-circular parts can swing around the rotation axis. Also, the inner contour parts of each of the pair of semi-circular parts are along the outer contour of the mirror part. Thereby, it is possible to suppress an increase in the gap between the first actuator and the movable mirror part. Therefore, the area utilization rate of the material for forming the MEMS mirror element can be improved. That is, the first actuator can be enlarged without enlarging the MEMS mirror element. Also, the yield of the material when forming the MEMS mirror element can be improved.

[0010] <3>The MEMS mirror element according to Aspect 3 of the present invention is the MEMS mirror element according to Aspect 1 or Aspect 2, wherein the second actuator includes cantilever portions provided in a pair on one side and the other side in a direction orthogonal to the rotation axis, with ends connected to the connection portions, and the shapes of the cantilever portions connected to the respective connection portions of the pair are symmetric to each other and along the outer contour of the first actuator.

[0011] According to the invention according to Aspect 3, the second actuator includes cantilever portions provided in a pair on one side and the other side in a direction orthogonal to the rotation axis, with ends connected to the connection portions. The shapes of the cantilever portions connected to the respective connection portions of the pair are symmetric to each other. Thereby, when the mirror portion swings by the second actuator, it is possible to suppress the swinging range of the mirror portion from being biased to one side or the other around the rotation axis. Also, the shapes of the cantilever portions connected to the respective connection portions of the pair are along the outer contour of the first actuator. Thereby, it is possible to suppress an increase in the gap between the second actuator and the first actuator. Therefore, the area utilization rate of the material forming the MEMS mirror element can be further improved. That is, without increasing the size of the MEMS mirror element, the size of the second actuator can be increased. Also, the material yield when forming the MEMS mirror element can be further improved.

[0012] <4>The MEMS mirror element according to Aspect 4 of the present invention is the MEMS mirror element according to any one of Aspects 1 to 3, wherein the first actuator and the second actuator swing in the same phase, and the mirror portion swings in a reverse phase to the first actuator and the second actuator.

[0013] According to the invention according to aspect 4, the first actuator and the second actuator oscillate in the same phase, and the mirror part oscillates in the opposite phase to the first actuator and the second actuator. Thereby, the mirror part and the first actuator and the second actuator can be caused to perform coupled oscillation. Therefore, for example, compared with the case where a MEMS mirror element includes one actuator for one movable mirror part, the amplitude when oscillating the mirror part can be made larger. Therefore, the amplitude of the mirror part can be made larger without taking measures such as lowering the frequency when oscillating the mirror part, miniaturizing the mirror part, or enlarging the MEMS mirror element as the size of the actuator increases. Furthermore, since the first actuator and the second actuator oscillate in the same phase, the stress generated in the connection part and the torsion bar can be reduced. Therefore, even when the amplitude of the mirror part is increased, it is possible to suppress a decrease in the durability of the MEMS mirror element.

[0014] <5>The MEMS mirror element according to aspect 5 of the present invention is the MEMS mirror element according to any one of aspects 1 to 4, wherein the first actuator and the second actuator are a piezoelectric thin film actuator including a lower electrode, a piezoelectric thin film disposed on the lower electrode, and an upper electrode disposed on the piezoelectric thin film, or an electromagnetic drive wiring structure for applying a current to perform electromagnetic drive.

[0015] According to the invention according to aspect 5, the first actuator and the second actuator include either a piezoelectric thin film actuator including a lower electrode, a piezoelectric thin film disposed on the lower electrode, and an upper electrode disposed on the piezoelectric thin film, or an electromagnetic drive wiring structure for applying a current to perform electromagnetic drive. As a result, the first actuator and the second actuator can operate to move perpendicular to the substrate on which the MEMS mirror element is disposed. That is, for example, by moving one side in the direction orthogonal to the rotation axis in the first actuator and the second actuator away from the substrate while moving the other side in the direction orthogonal to the rotation axis closer to the substrate, the first actuator and the second actuator can be rotated about the rotation axis. Further, by periodically changing the direction in which the first actuator and the second actuator are rotated as described above, the first actuator and the second actuator can be oscillated about the rotation axis.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a MEMS mirror element capable of increasing the amplitude of the mirror without taking measures such as reducing the frequency when oscillating the mirror, miniaturizing the mirror, increasing the size of the MEMS mirror element as the size of the actuator increases, and the like.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0018] Hereinafter, with reference to the drawings, a MEMS mirror element according to an embodiment of the present invention will be described. The MEMS mirror element according to this embodiment is used in, for example, an AR device or a VR device. For example, the MEMS mirror element according to this embodiment is provided on smart glasses. The MEMS mirror element provided on the smart glasses sweeps the laser light irradiated from a light source (not shown) across the lens of the smart glasses. By doing this, figures, characters, etc. that are visible to the user of the smart glasses are drawn on the lens of the smart glasses.

[0019] (Structure of MEMS Mirror Element) FIG. 1 is a perspective view of a MEMS mirror element 1 according to an embodiment. FIG. 2 is a schematic diagram showing the oscillation of the mirror part 11 as viewed along the rotation axis S. FIG. 3 is an enlarged view of part III shown in FIG. 1. As shown in FIG. 1, the MEMS mirror element 1 includes a movable mirror part 10, a first actuator 20, a second actuator 30, and a frame 40. In this embodiment, the MEMS mirror element 1 having the above-described respective configurations is arranged on a substrate CB provided in the above-described respective devices.

[0020] (Regarding the Movable Mirror Part) The movable mirror unit 10 is located at the center of the MEMS mirror element 1, for example, as shown in FIG. 1. The movable mirror unit 10 includes a mirror unit 11 and a torsion bar 12. The mirror unit 11 is formed in a disk shape, for example, as shown in FIG. 1. In the present embodiment, the mirror unit 11 swings around the rotation axis S shown in FIGS. 1 and 2 by each of the following configurations. In the present embodiment, the rotation axis S passes through the center of the mirror unit 11. The rotation axis S is parallel to the radial direction of the mirror unit 11. In the present embodiment, when the mirror unit 11 swings, as shown in FIG. 2, it means that the mirror unit 11 alternately rotates in the first rotation direction R1, which is one direction around the rotation axis S, and the second rotation direction R2, which is the direction opposite to the first rotation direction R1. The same applies when the first actuator 20 and the second actuator 30 swing. In the MEMS mirror element 1 according to the present embodiment, the mirror unit 11 swings around the rotation axis S to scan the laser beam. Details of the swing of the mirror unit 11 or the scanning of the laser beam will be described later.

[0021] One end of the torsion bar 12 is connected to the mirror unit 11. The torsion bar 12 extends along the rotation axis S. The other end of the torsion bar 12 is connected to a connection portion 41 of a frame 40, which will be described later, as shown in FIG. 3. As shown in FIG. 1, a pair of torsion bars 12 are provided on both sides in the radial direction of the mirror unit 11. Therefore, a pair of connection portions 41 of the frame 40 are also provided in the same manner. Other details of the connection portion 41 will be described later. The torsion bar 12 provided in this way supports the mirror unit 11 so as to be swingable around the rotation axis S. The torsion bar 12 deforms so as to be twisted in accordance with the rotation of the mirror unit 11 around the rotation axis S.

[0022] (Regarding the first actuator) The first actuator 20 swings the mirror unit 11 around the rotation axis S. Specifically, the first actuator 20 swings around the rotation axis S when an alternating voltage is applied. Thus, the first actuator 20, together with the second actuator 30, swings the mirror unit 11 around the rotation axis S by a coupled oscillation. The first actuator 20 is connected to a pair of connection parts 41 and is disposed around the movable mirror unit 10. The first actuator 20 in the present embodiment is, for example, a so-called ring-shaped actuator. Specifically, the first actuator 20 has the following configuration.

[0023] That is, the first actuator 20 includes two semi-annular parts 21. As shown in FIG. 1, each semi-annular part 21 includes a semi-circular outer contour part 21a and an inner contour part 21b, and a straight part 21c that connects the respective ends of the outer contour part 21a and the inner contour part 21b to each other. In the present embodiment, the straight part 21c of the semi-annular part 21 is disposed along the torsion bar 12. That is, the size of the gap between the straight part 21c of the semi-annular part 21 and the torsion bar 12 is constant over the longitudinal direction of the torsion bar 12. Further, in the present embodiment, the inner contour part 21b of the semi-annular part 21 is formed along the outer contour of the mirror unit 11. That is, the size of the gap between the inner contour part 21b of the semi-annular part 21 and the outer contour of the mirror unit 11 is constant over the circumferential direction of the mirror unit 11. This suppresses an increase in the gap between the semi-annular part 21 and the movable mirror unit 10. Both ends of the semi-annular part 21 in the direction along the rotation axis S are connected to the connection parts 41 as shown in FIG. 3. The connection configuration between the semi-annular part 21 and the connection parts 41 shown in FIG. 3 is the same for each of the pair of connection parts 41. The semi-annular parts 21 having the above-described configuration are provided in a pair on one side and the other side in the direction orthogonal to the rotation axis S as shown in FIG. 1. Thus, the first actuator 20 which is a ring-shaped actuator is formed. In the present embodiment, the fact that the first actuator 20 swings around the rotation axis S may mean that each of the pair of semi-circular portions 21 alternately approaches and separates with respect to the substrate CB to which the MEMS mirror element 1 is attached.

[0024] (Regarding the second actuator) The second actuator 30 swings the mirror part 11 around the rotation axis S. Specifically, the second actuator 30 swings around the rotation axis S when an alternating voltage is applied. Thus, the second actuator 30, together with the first actuator 20, swings the mirror part 11 around the rotation axis S by a coupled vibration. The second actuator 30 is connected to the pair of connection parts 41 and is disposed around the movable mirror part 10 and the first actuator 20. The second actuator 30 in the present embodiment is, for example, a so-called fork type actuator. Specifically, the second actuator 30 has the following configuration.

[0025] That is, the second actuator 30 includes four cantilever parts 31. As shown in FIG. 1, the cantilever part 31 is formed in a substantially right-angled triangular shape. That is, the cantilever part 31 has a shape in which a portion corresponding to the hypotenuse of the right-angled triangle is arc-shaped. Hereinafter, the arc-shaped portion of the cantilever part 31 is referred to as an arc hypotenuse part 31a. Also, a linear portion corresponding to a side other than the hypotenuse of the cantilever part 31 formed in a substantially right-angled triangular shape is referred to as a linear part 31b. In this embodiment, the straight portion 31b of the cantilever portion 31 is arranged along the inner contour portion 40b of the frame 40 described later. That is, the size of the gap between the straight portion 31b of the cantilever portion 31 and the inner contour portion 40b of the frame 40 is constant over the longitudinal direction of the straight portion 31b of the cantilever portion 31. Further, in this embodiment, the arc hypotenuse portion 31a of the cantilever portion 31 is formed along the outer contour of the first actuator 20, that is, the outer contour portion 21a. That is, the size of the gap between the arc hypotenuse portion 31a and the outer contour portion 21a is constant over the circumferential direction of the first actuator 20. This suppresses an increase in the gap between the cantilever portion 31 and the first actuator 20 and the frame 40. One end of the arc hypotenuse portion 31a of the cantilever portion 31 is connected to the connection portion 41 as shown in FIG. 3. As shown in FIG. 1, the cantilever portion 31 having the above-described configuration is provided in a pair on one side and the other side in the direction orthogonal to the rotation axis S. That is, two of the four cantilever portions 31 are provided in a pair around the rotation axis S on one connection portion 41. Such a shape or structure is provided symmetrically with respect to each other on one side and the other side of the pair of connection portions 41. That is, in this embodiment, the shapes of the cantilever portions 31 connected to each of the pair of connection portions 41 are symmetric with respect to each other. Thus, the second actuator 30 which is a fork type actuator is formed. In this embodiment, the fact that the second actuator 30 swings around the rotation axis S may mean that each of the pair of cantilever portions 31 repeatedly approaches and separates alternately with respect to the substrate CB to which the MEMS mirror element 1 is attached. In this embodiment, of the four cantilever portions 31, the two provided on one side in the direction orthogonal to the rotation axis S move in the same direction as each other, and the two provided on the other side move in the same direction as each other.

[0026] (Regarding the form of the actuator) In the present embodiment, the first actuator 20 and the second actuator 30 are, for example, piezoelectric thin film actuators. That is, the first actuator 20 and the second actuator 30 include a lower electrode, a piezoelectric thin film disposed on the lower electrode, and an upper electrode disposed on the piezoelectric thin film. Such first actuator 20 and second actuator 30 are formed, for example, by patterning a material substrate MB having each of the above-described configurations. Alternatively, the first actuator 20 and the second actuator 30 may be formed, for example, by an electromagnetic drive wiring structure for applying a current and performing electromagnetic drive. Or, as long as the first actuator 20 and the second actuator 30 are configured to be able to alternately approach and separate each of one and the other in a direction orthogonal to the rotation axis S with respect to the substrate CB to which the MEMS mirror element 1 is attached, any other structure may be appropriately used.

[0027] In the present embodiment, both the first actuator 20 and the second actuator 30 are piezoelectric thin film actuators. In the present embodiment, the first actuator 20 and the second actuator 30 are integrally formed together with each configuration included in the other MEMS mirror element 1 (details will be described later). Not limited to this, for example, both the first actuator 20 and the second actuator 30 may be formed by an electromagnetic drive wiring structure. Alternatively, one of the first actuator 20 and the second actuator 30 may be formed by a piezoelectric thin film actuator, and the other may be formed by an electromagnetic drive wiring structure.

[0028] (Regarding the frame) The frame 40 is a frame-shaped portion disposed around the movable mirror portion 10, the first actuator 20, and the second actuator 30. As shown in FIG. 1, the frame 40 includes a rectangular outer contour portion 40a and an inner contour portion 40b, respectively, and a connection portion 41 that protrudes from the inner contour portion 40b toward the inside of the frame 40. The outer frame portion 40a and the inner frame portion 40b form the frame 40 in a frame shape. In the present embodiment, the frame 40 is square. In the present embodiment, the four sides of each of the outer frame portion 40a and the inner frame portion 40b are parallel to each other. Two of the four sides of each of the outer frame portion 40a and the inner frame portion 40b are positioned parallel to the rotation axis S, and the other two sides are positioned perpendicular to the rotation axis S.

[0029] (Regarding the connection portion of the frame) The connection portion 41 is a portion that protrudes inside the frame 40 along the rotation axis S from the center of two sides of the inner frame portion 40b that are positioned perpendicular to the rotation axis S. The connection portions 41 are provided in a pair on two sides that are positioned perpendicular to the rotation axis S. In the present embodiment, the following configurations are respectively connected to the pair of connection portions 41. Each connection structure in each of the pair of connection portions 41 is the same as each other. Hereinafter, one connection structure of the pair of connection portions 41 shown in FIG. 3 will be described, and the description of the other will be omitted.

[0030] The other end of the torsion bar 12 is connected to the connection portion 41. At this time, the other end of the torsion bar 12 is connected to the tip of the connection portion 41 protruding from the inner frame portion 40b as shown in FIG. 3. One end of each of the semi-circular portions 21 of the first actuator 20 provided in a pair in the one and the other directions perpendicular to the rotation axis S is connected to the connection portion 41. The end of the semi-circular portion 21 is connected to a portion far from the inner frame portion 40b of the side surface facing in the direction perpendicular to the rotation axis S in the connection portion 41. At this time, as shown in FIG. 3, an electrode E disposed on the upper surface between the outer frame portion 40a and the inner frame portion 40b of the frame 40 is connected to the semi-circular portion 21 positioned in one direction perpendicular to the rotation axis S. In the present embodiment, the electrode E is disposed on the material substrate MB of the MEMS mirror element 1 and formed by patterning (details will be described later). The connecting portion 41 is connected to the ends of the cantilever portion 31 of the second actuator 30 provided in a pair on one side and the other side in the direction orthogonal to the rotation axis S, that is, one end of the arc bevel portion 31a. The end of the cantilever portion 31 is connected to a portion close to the inner contour portion 40b of the frame 40 among the side surfaces facing the direction orthogonal to the rotation axis S in the connecting portion 41. At this time, as shown in FIG. 3, an electrode E disposed on the upper surface between the outer contour portion 40a and the inner contour portion 40b of the frame 40 is connected to each of the cantilever portions 31. With the above-described respective configurations, the MEMS mirror element 1 according to the present embodiment is configured.

[0031] (Regarding the swing of the mirror portion) Next, the swing of the mirror portion 11 in the movable mirror portion 10 will be described. As described above, in the MEMS mirror element 1 according to the present embodiment, as shown in FIGS. 1 and 2, the mirror portion 11 of the movable mirror portion 10 swings around the rotation axis S. By this, the laser light irradiated from a light source (not shown) is scanned. More specifically, by swinging, the mirror portion 11 reflects the incident light Li, which is the laser light irradiated from a light source (not shown) to the mirror portion 11, as the reflected light Lr outward. Note that the direction of the reflected light Lr changes as the mirror portion 11 swings. As described above, the MEMS mirror element 1 according to the present embodiment scans the laser light with the reflected light Lr whose direction changes due to the swing of the mirror portion 11.

[0032] Here, as shown in FIG. 2, the reflected light Lr when the mirror portion 11 rotates most in the first rotation direction R1 is referred to as the first reflected light Lr1. The reflected light Lr when the mirror portion 11 rotates most in the second rotation direction R2 is referred to as the second reflected light Lr2. In the present embodiment, the first optical scanning angle θ1, which is the relative angle between the incident light Li and the first reflected light Lr1, and the second optical scanning angle θ2, which is the relative angle between the incident light Li and the second reflected light Lr2, are equal. By this, it is preferable to prevent a bias from occurring in the direction of the reflected light Lr reflected by the mirror portion 11. In order to satisfy the above, in the present embodiment, the angle by which the mirror unit 11 can rotate from the initial position in the first rotation direction R1 and the angle by which the mirror unit 11 can rotate from the initial position in the second rotation direction R2 are equal. Note that the initial position of the mirror unit 11 is the position where the mirror unit 11 is not rotating around the rotation axis S.

[0033] In the present embodiment, the amplitude when the mirror unit 11 swings is represented by the relative angle between the first reflected light Lr1 and the second reflected light Lr2 in FIG. 2. Hereinafter, in the present embodiment, as shown in FIG. 2, the relative angle between the first reflected light Lr1 and the second reflected light Lr2, which represents the amplitude when the mirror unit 11 swings, is referred to as the optical scanning angle θ. The range in which the laser beam is scanned by the MEMS mirror element 1 is determined by the optical scanning angle θ. Note that the change amount of the relative angle between the incident light Li and the reflected light Lr is twice the angle by which the mirror unit 11 has rotated. That is, for example, the first optical scanning angle θ1 is twice the rotation angle when the mirror unit 11 rotates most in the first rotation direction R1 from the initial position.

[0034] Here, in the MEMS mirror element 1, it is preferable to ensure a sufficient optical scanning angle θ while suppressing the miniaturization of the mirror unit 11 and the enlargement of the MEMS mirror element 1. However, if the size of the actuator is not sufficient, the force for swinging the mirror unit 11 cannot be obtained sufficiently, and a sufficient optical scanning angle θ cannot be obtained. Therefore, in the present embodiment, the mirror unit 11 swings around the rotation axis S by the coupled vibration generated when the first actuator 20 and the second actuator 30 swing around the rotation axis S. That is, two actuators are provided for one mirror unit 11. Thereby, the force for swinging the mirror unit 11 is made sufficient.

[0035] The rocking of the first actuator 20 and the second actuator 30 is performed by applying an alternating voltage to each of the first actuator 20 and the second actuator 30. That is, by applying an alternating voltage to the semi-circular portion 21 of the first actuator 20 and the cantilever portion 31 of the second actuator 30, an electromagnetic force whose direction changes periodically is generated. As a result, each of the semi-circular portion 21 and the cantilever portion 31 repeats approaching and separating from the substrate CB to which the MEMS mirror element 1 is attached. Thus, the first actuator 20 and the second actuator 30 rock.

[0036] (Regarding the optical scanning angle of the MEMS mirror element) FIG. 4 is a graph showing the relationship between the voltage applied to the MEMS mirror element 1 and the optical scanning angle θ. In the graph of FIG. 4, the horizontal axis represents the voltage (V) applied to the MEMS mirror element 1, and the vertical axis represents the magnitude of the optical scanning angle θ (°) corresponding to the applied voltage. Note that the results shown in FIG. 4 are for the case where one side of the outer peripheral portion 40a of the frame 40 is 3.8 mm and the diameter of the mirror portion 11 is 1 mm in the MEMS mirror element 1 according to the present embodiment. As shown in FIG. 4, as the voltage applied to the MEMS mirror element 1 increases, the optical scanning angle θ increases. In the present embodiment, when a voltage of 25 V was applied to the MEMS mirror element 1 and the first actuator 20 and the second actuator 30 were operated, the optical scanning angle θ became 40.0°. Here, in the MEMS mirror element 1 according to the present embodiment, when only the second actuator 30, which is a fork-type actuator, was operated, the optical scanning angle θ became 11.5°. Also, in the MEMS mirror element 1 according to the present embodiment, when only the first actuator 20, which is a ring-type actuator, was operated, the optical scanning angle θ became 29.1°. Thus, it was confirmed that when the mirror unit 11 is swung by the two actuators of the first actuator 20 and the second actuator 30, the optical scanning angle θ can be made larger than when the mirror unit 11 is swung by one actuator.

[0037] (Regarding the stress acting on the MEMS mirror element) Here, the MEMS mirror element 1 according to the present embodiment is integrally formed by patterning a material substrate MB. For this reason, when the mirror unit 11, the first actuator 20, and the second actuator 30 swing, stress acts due to the deformation of the torsion bar 12 of the movable mirror unit 10 and the connection portion 41 of the frame 40. When the optical scanning angle θ of the mirror unit 11 increases, or when the frequency at which the mirror unit 11 swings increases, stress concentration occurs in the torsion bar 12 and the connection portion 41, which may cause mechanical failure in the MEMS mirror element 1. In the present embodiment, in order to suppress mechanical failure of the MEMS mirror element 1, it is required that the stress acting on the MEMS mirror element 1 be 7 GPa or less. In order to suppress the above-described mechanical failure, in the present embodiment, the mirror unit 11, the first actuator 20, and the second actuator 30 swing as follows.

[0038] That is, in the present embodiment, when each of the mirror unit 11, the first actuator 20, and the second actuator 30 swings, the first actuator 20 and the second actuator 30 swing in the same phase. And the mirror unit 11 swings in a reverse phase to the first actuator 20 and the second actuator 30. By this, stress concentration in the torsion bar 12 and the connection portion 41 is suppressed, and mechanical failure of the MEMS mirror element 1 is suppressed.

[0039] FIG. 5 is an analysis diagram showing a case where the first actuator 20 and the second actuator 30 swing in a reverse phase. FIG. 6 is an analysis diagram showing the magnitude of stress generated around the connection portion 41 when the first actuator 20 and the second actuator 30 are oscillated in opposite phases. As shown in FIG. 5, when the first actuator 20 and the second actuator 30 are oscillated in opposite phases, stress concentration occurs at the connection portion 41 as shown in FIG. 6. When the first actuator 20 and the second actuator 30 are oscillated in opposite phases and the MEMS mirror element 1 is at the optical scanning angle of 45°, it was confirmed that the maximum stress value in the MEMS mirror element 1 becomes 10 GPa at the connection portion 41, and there is a high possibility of mechanical failure.

[0040] FIG. 7 is an analysis diagram showing the case where the first actuator 20 and the second actuator 30 are oscillated in the same phase. FIG. 8 is an analysis diagram showing the magnitude of stress generated around the connection portion 41 when the first actuator 20 and the second actuator 30 are oscillated in the same phase. As shown in FIG. 7, when the first actuator 20 and the second actuator 30 are oscillated in the same phase, stress concentration at the connection portion 41 is suppressed as shown in FIG. 8. Also, the stress confirmed in the analysis result shown in FIG. 8 was acting on the torsion bar 12. When the first actuator 20 and the second actuator 30 are oscillated in the same phase and the MEMS mirror element 1 is at the optical scanning angle of 45°, it was confirmed that the maximum stress value in the MEMS mirror element 1 becomes 2 GPa at the torsion bar 12, and mechanical failure can be suppressed.

[0041] (Regarding the manufacturing process of the MEMS mirror element) Next, the manufacturing process of the MEMS mirror element 1 according to the present embodiment will be described with reference to FIGS. 9 to 12. FIG. 9 is a first diagram showing the manufacturing process of the MEMS mirror element 1. FIG. 10 is a second diagram showing the manufacturing process of the MEMS mirror element 1. FIG. 11 is a third diagram showing the manufacturing process of the MEMS mirror element 1. FIG. 12 is a fourth diagram showing the manufacturing process of the MEMS mirror element 1.

[0042] The MEMS mirror element 1 according to the present embodiment is formed by a standard MEMS process using a single material substrate MB. That is, each component included in the MEMS mirror element 1 according to the present embodiment is integrally formed by processing a single material substrate MB as follows. As shown in FIG. 9, the material substrate MB includes an SOI substrate L1, an insulating film L2, a lower electrode L3, a piezoelectric thin film L4, and an upper electrode L5. The SOI substrate L1 is the portion that contacts the substrate CB when the MEMS mirror element 1 is attached to the substrate CB. A commercially available SOI substrate L1 is preferably used. The SOI substrate L1 is formed by laminating a silicon support layer L1a, a buried oxide film L1b, and a silicon device layer L1c from the side close to the substrate CB. In the present embodiment, the thickness of the silicon support layer L1a is, for example, 400 μm. The thickness of the buried oxide film L1b is, for example, 1 μm. The thickness of the silicon device layer L1c is, for example, 50 μm.

[0043] The insulating film L2 is provided to insulate the SOI substrate L1 and the lower electrode L3. The lower electrode L3 forms, for example, the movable mirror portion 10. The piezoelectric thin film L4 and the upper electrode L5 form, for example, the electrodes E in the first actuator 20 and the second actuator 30. The insulating film L2, the lower electrode L3, the piezoelectric thin film L4, and the upper electrode L5 are formed, for example, by appropriately laminating various materials on a commercially available SOI substrate L1.

[0044] First, the insulating film L2, the lower electrode L3, the piezoelectric thin film L4, and the upper electrode L5 are formed on the SOI substrate L1 to form the material substrate MB shown in FIG. 9. Next, as shown in FIG. 10, the lower electrode L3, the piezoelectric thin film L4, and the upper electrode L5 are patterned by photolithography and etching. Thereby, for example, the electrodes E in the first actuator 20 and the second actuator 30 are formed. Next, as shown in FIG. 11, the silicon device layer L1c is patterned by deep reactive ion etching (DRIE) of silicon. By this, for example, the movable mirror portion 10 is formed. Then, as shown in FIG. 12, the silicon support layer L1a is patterned by deep reactive ion etching of silicon, and the unnecessary silicon support layer L1a is removed. Finally, etching is performed with CHF3 plasma to remove the unnecessary buried oxide film L1b. Through the above steps, the MEMS mirror element 1 according to the present embodiment is formed.

[0045] As described above, according to the MEMS mirror element 1 according to the present embodiment, the first actuator 20 disposed around the movable mirror portion 10 and the second actuator 30 disposed around the movable mirror portion 10 and the first actuator 20 are provided. That is, the MEMS mirror element 1 includes two actuators for one movable mirror portion 10. Thereby, for example, compared with the case where the MEMS mirror element 1 includes one actuator for one movable mirror portion 10, the force for swinging the mirror portion 11 can be increased. Therefore, for example, the speed when the mirror portion 11 swings can be increased. Accordingly, the amplitude of the mirror portion 11 can be increased without taking measures such as lowering the frequency when swinging the mirror portion 11, miniaturizing the mirror portion 11, and increasing the size of the MEMS mirror element 1 as the size of the actuator increases.

[0046] Further, the first actuator 20 includes semi-circular portions 21 provided in a pair on one side and the other side in a direction orthogonal to the rotation axis S. Both ends of each of the pair of semi-circular portions 21 in the direction along the rotation axis S are connected to each of the pair of connection portions 41. Thereby, each of the semi-circular portions 21 can swing around the rotation axis S. In addition, the inner contour portions 21b of each of the pair of semi-circular portions 21 are along the outer contour of the mirror portion 11. Thereby, it is possible to suppress an increase in the gap between the first actuator 20 and the movable mirror portion 10. Therefore, the area utilization rate of the material for forming the MEMS mirror element 1 can be improved. That is, the first actuator 20 can be enlarged without enlarging the MEMS mirror element 1. In addition, the material yield when forming the MEMS mirror element 1 can be improved.

[0047] In addition, the second actuator 30 includes cantilever portions 31 provided in a pair on one side and the other side in a direction orthogonal to the rotation axis S, with the ends connected to the connection portions 41. The shapes of the cantilever portions 31 connected to each of the pair of connection portions 41 are symmetric to each other. Thereby, when the mirror portion 11 swings by the second actuator 30, it is possible to suppress the swinging range of the mirror portion 11 from being biased to one side or the other side around the rotation axis S. In addition, the shapes of the cantilever portions 31 connected to each of the pair of connection portions 41 are along the outer contour of the first actuator 20. Thereby, it is possible to suppress an increase in the gap between the second actuator 30 and the first actuator 20. Therefore, the area utilization rate of the material for forming the MEMS mirror element 1 can be further improved. That is, the second actuator 30 can be enlarged without enlarging the MEMS mirror element 1. In addition, the material yield when forming the MEMS mirror element 1 can be further improved.

[0048] Further, the first actuator 20 and the second actuator 30 oscillate in the same phase, and the mirror unit 11 oscillates in a phase opposite to that of the first actuator 20 and the second actuator 30. Thereby, the mirror unit 11 and the first actuator 20 and the second actuator 30 can be made to oscillate in a coupled manner. Thus, for example, compared with the case where the MEMS mirror element 1 includes one actuator for one movable mirror unit 10, the amplitude when oscillating the mirror unit 11 can be made larger. Therefore, the amplitude of the mirror unit 11 can be made larger without taking measures such as reducing the frequency when oscillating the mirror unit 11, miniaturizing the mirror unit 11, or increasing the size of the MEMS mirror element 1 as the size of the actuator increases. Furthermore, since the first actuator 20 and the second actuator 30 oscillate in the same phase, the stress generated in the connection portion 41 and the torsion bar 12 can be reduced. Thus, even when the amplitude of the mirror unit 11 is increased, it is possible to suppress a decrease in the durability of the MEMS mirror element 1.

[0049] Also, the first actuator 20 and the second actuator 30 include either a piezoelectric thin film actuator including a lower electrode L3, a piezoelectric thin film L4 disposed on the lower electrode L3, and an upper electrode L5 disposed on the piezoelectric thin film L4, or an electromagnetic drive wiring structure for applying a current to perform electromagnetic drive. Thereby, the first actuator 20 and the second actuator 30 can be operated to move perpendicularly to the substrate CB on which the MEMS mirror element 1 is disposed. That is, for example, while moving one side in the direction orthogonal to the rotation axis S in the first actuator 20 and the second actuator 30 away from the substrate CB, and moving the other side in the direction orthogonal to the rotation axis S closer to the substrate CB, the first actuator 20 and the second actuator 30 can be rotated about the rotation axis S. Also, by periodically changing the direction of rotation of the first actuator 20 and the second actuator 30 as described above, the first actuator 20 and the second actuator 30 can be oscillated about the rotation axis S.

[0050] Note that the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, although the first actuator 20 has been described as a so-called ring-type actuator and the second actuator 30 has been described as a so-called fork-type actuator, it is not limited thereto. That is, for example, the first actuator 20 may be a fork-type actuator and the second actuator 30 may be a ring-type actuator. Alternatively, both the first actuator 20 and the second actuator 30 may be ring-type actuators, or both the first actuator 20 and the second actuator 30 may be fork-type actuators.

[0051] In addition, within the scope not departing from the spirit of the present invention, it is possible to appropriately replace the components in the above-described embodiments with well-known components, and the above-described modification examples may also be appropriately combined.

Explanation of Reference Numerals

[0052] 1 MEMS mirror element 10 Movable mirror part 11 Mirror part 12 Torsion bar 20 First actuator 21 Semi-circular part 21a Outer contour part 21b Inner contour part 21c Straight part 30 Second actuator 31 Cantilever part 31a Arc bevel part 31b Straight part 40 Frame 40a Outer contour part 40b Inner contour part 41 Connection part CB Substrate E Electrode L1 SOI substrate L1a Silicon support layer L1b Oxide film L1c Silicon device layer L2 Insulating film L3 Lower electrode L4 Piezoelectric thin film L5 Upper electrode Li Incident light Lr Reflected light Lr1 First reflected light Lr2 Second reflected light MB Material substrate R1 First rotation direction R2 Second rotation direction S Rotation axis θ Optical scanning angle θ1 First optical scanning angle θ2 Second optical scanning angle

Claims

1. A movable mirror unit including a mirror unit, and a pair of torsion bars that support the mirror unit so as to be swingable about a rotation axis, the torsion bars each having one end connected to the mirror unit and extending along the rotation axis; A pair of connection parts to which the other ends of the pair of torsion bars are connected; A first actuator connected to the pair of connection parts and disposed around the movable mirror unit; A second actuator connected to the pair of connection parts and disposed around the movable mirror unit and the first actuator; Comprising; A MEMS mirror element characterized by the above.

2. The first actuator includes a pair of semi-circular parts provided on one side and the other side in a direction orthogonal to the rotation axis, Both ends of each of the pair of semi-circular parts in the direction along the rotation axis are connected to each of the pair of connection parts, The inner contour of each of the pair of semi-circular parts follows the outer contour of the mirror unit, The MEMS mirror element according to claim 1, characterized by the above.

3. The second actuator includes a pair of cantilever parts provided on one side and the other side in a direction orthogonal to the rotation axis, with ends connected to the connection parts, The shapes of the pair of cantilever parts connected to each of the pair of connection parts are symmetric to each other and follow the outer contour of the first actuator, The MEMS mirror element according to claim 1, characterized by the above.

4. The first actuator and the second actuator swing in the same phase, The mirror unit swings in a reverse phase to the first actuator and the second actuator, The MEMS mirror element according to any one of claims 1 to 3, characterized by the above.

5. The first actuator and the second actuator each include either a piezoelectric thin film actuator including a lower electrode, a piezoelectric thin film disposed on the lower electrode, and an upper electrode disposed on the piezoelectric thin film, or an electromagnetic drive wiring structure for applying a current to perform electromagnetic drive; The MEMS mirror element according to any one of claims 1 to 3, characterized by the above.

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